The Federal Communications Commission has required television broadcasters to transition from their current National Television System Committee (NTSC) analog antenna systems to DTV antenna systems. DTV technology allows for the transmission of television programming having higher resolution pictures and better sound quality than NTSC analog antenna systems. DTV systems also allow broadcasters to transmit more than one signal per channel, and thus, deliver more than one television program per station.
Test receivers exist for identifying problems in the transmission of a DTV signal from the DTV transmitting antenna to a particular point of reception, but problems can also occur in the transmission of the DTV signal from a DTV transmitter to the DTV transmitting antenna that prevent a signal generated by the DTV transmitter from reaching the DTV transmitting antenna.
Echoes are reflected signals that occur when the impedance is not properly matched between components of the DTV transmitting system and can be an indicator of potential problems in the transmission of a DTV signal. The echo/reflected signals “add to” or “subtract from” the signal being transmitted from the DTV transmitter to the DTV transmitting antenna, and, as such, increase or decrease the level of the DTV signal. Although echoes commonly occur during the transmission of a DTV signal, they will cause problems if their magnitude increases to a level that interferes with the transmission of the DTV signal.
When echo levels exceed an acceptable threshold, the signal received by the transmitting DTV antenna may differ greatly from the original signal that was sent by the DTV transmitter. The echoes may even cause the DTV signal and/or sound corresponding to a television program to be lost completely, and disrupt television service to a viewer. Testing devices are needed to analyze the performance of a DTV antenna transmitting system from the DTV transmitter to the transmitting antenna, and to provide data about the performance of the DTV antenna transmitting system, so that failures can be avoided. Methods exist for testing DTV transmitting systems that are capable of identifying whether or not echoes are occurring within a transmitting system. The conventional method of testing DTV transmitting systems requires going off-air and shutting down the DTV transmitting system, which can be costly, to connect the testing device to the transmission line. The conventional method of testing DTV transmitting systems utilizes a testing device, such as a network analyzer, that is connected to the transmission line via a connector/adapter. A low power test signal is then sent by the transmitter, and the network analyzer analyzes the signal received. The network analyzer is able to ascertain the magnitude of the problem (i.e., how much of the test signal was lost up to the point at which the network analyzer is connected) and the source or location of the signal loss. However, the network analyzer cannot be utilized to test DTV transmitting systems in real time while operating under full power. Additionally, the network analyzer is limited to a resolution of approximately a hundred feet if used with 6 MHz bandwidth, and thus unable to identify potential problems that are less than a hundred feet apart.
Another method of testing DTV antenna systems is described in U.S. Pat. No. 6,212,286 to Rott et al. (hereafter “Rott”) which discloses a method of testing a DTV antenna transmitting system in real time and under full power. Rott involves a method for testing an antenna system that enables the source/location of a problem to be identified by aiming an infrared camera at the component of the transmitting system to be tested while the component is in full operation.
The infrared camera records a thermal image of the test object. When the temperature of a portion of the thermal image is extremely high when compared to the remainder of the thermal image, the portion of the test object corresponding to the high temperature area on the thermal image is likely to be the source of the problem. Typically, a sharp increase in temperature is an indicator of a malfunctioning component. Thus, the area of the thermal image where there is a temperature increase can be matched to the area of the component that was tested.
The thermal image generated from the testing method of Rott reveals extreme temperature gradients. If an echo is created, that only causes a small increase in temperature, the echo may go undetected by the infrared camera of Rott. As a result, DTV service to consumers may be interrupted by the effects of the undetected echo signal.
Accordingly, it is desirable to provide a real time method for testing DTV antenna transmitting systems from the DTV transmitter to the DTV transmitting antenna that is operable under full power.
Further, it is desirable to provide a method for real time testing of DTV antenna transmitting systems that can identify the magnitude and the location of existing and/or potential problems.
Further, it is desirable to provide a method for testing a DTV antenna transmitting system that minimizes time and cost in identifying and resolving a problem that occurs within a DTV antenna transmitting system.